Detection and Measurement Techniques - Belgische ... · PDF fileDetection and Measurement...

© SCK•CEN Academy

I. Majkowski

[email protected]

Detection and Measurement

Techniques


When to use measurement techniques ?

Measurements methods

Direct (α, β en γ)

Indirect (destructive)

Pre-characterisation

Development of measurement strategy

Detection and Measurement Techniques Content

2


Purpose

Establish the isotopic vector (finger print) & their dispersion

Listing all rooms & material

How ?

History of the installation including incidents (interview ‘previous’ workers)

Term source (list of isotopes)

Code to calculate activation in various material

Code to evaluate the dispersion of the radioactivity in the installation

Measure the nuclides (Also DTM) to ‘validate’ the Isotopic vector and the

dispersion/activation profiles

Key nuclide (scaling factor – level of conservatism):

Cs-137 Fission product, Sr-90 (pure beta)

Co-60 Activation product (H-3 (pure low beta)– higher mobility); C-14 (pure beta),

Fe-55, Ni-63 (pure beta), Mn-54, Ag-108m, Ag-110m, Sb-125, Cs-134, Ba-133, Eu-

152, Eu-154, Eu-155

Am-241 (gamma), Pu-241 (beta): Actinides (U, Pu, Cm,..)

.

When to use measurement techniques ? Phase 1: pre-characterisation

3


Based on the pre-characterisation

Grouping (measurement techniques in mind), per:

Area/zone of the same use; history

Fixe (building – concrete) – mobile (dismantle - metal)

Isotopic vector (fingerprint) – activated or not

Type of material (geometry, physiochemical form)

… That are candidate for Clearance

For each group: Define the clearance measurements to verify

compliance to Clearance level

When to use measurement techniques? Phase 2: Clearance measurement

4


Direct measurements

Alpha & beta (Used as illustration for statistics & parameters)

Gamma

Indirect/destructive measurements

Taking the sample

Treating the sample

Measuring the sample

General remark

Lots of monitors/systems are available on market

Smart, Black box (algorithm,… )

Measurement methods

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Gas detector

Capture electron (Ionisation) – Mostly Prop. mode

Sealed OR Compensation gas (need a ‘loading station’)

Less sensitive to gamma background

Scintillation

Collect the light (excitation) by PM

Light seal – clear when broken

Easy to handle

Passivated Implanted Planar Silicon

(PIPS) - semiconductor

Surface very small

Delicate

Direct measurement of alpha en beta Hand-held monitor

6


HV setup before calibration

Max efficiency

Min interference between

channels

Usually 0.1 - 1 % beta in alpha

channel

Problem in pre-characterisation

40 Bq/cm² (0.4 Bq/cm² - 100 times

limit)

0.4 Bq/cm² (0.04 Bq/cm² - 10

times limit) of non existing alpha

Hand-held monitor alpha en beta First trap – High voltage (calibration)

7

0

10

20

30

40

50

60

70

80

0 200 400 600 800 1000 1200 1400

Sourca alpha

HV

cps

canal bêta

canal alpha

0

10

20

30

40

50

60

70

80

0 200 400 600 800 1000 1200 1400

canal bêta

Source bêta

HV

canal alpha

cps

Dremple

Pulse hight

Time

channel

channel


The min detectable energy: starts to be difficult from below C-14 (about 160

keV) & impossible for H-3 (18 keV) (Except with open window)

DTM: Low beta energy (H-3), pure gamma emitters (used in medical).

Hand-held monitor alpha en beta Detectors

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Scintil.

Electra

(β)

Scintil.

Electra

(α+β)

Scintil.

Como

(α+β)

Scintil.

Berth. (α+β

– Ag sci)

Gas

Contam.

(α+β)

Surface cm² 100/600 100/600 170 170 166

Window 1.2 mg/cm² 1.2 mg/cm² 0.4 mg/cm²

C-14 (rend.) 7% 1% 7% 5% 11%

Co-60 (rend.) 15% 10% 14% 15% 17%

Cs-137 (rend.) 20% 15% 17% 21% 20%

Cl-36 (rend.) 25% 20% 20% 22% 20%

Am-241 (rend.) / 16% 11% 10% 13%

Gamma

1 µSv/h

cps (α)

20 cps (β)

cps (α)

20 cps (β)

cps (α)

100 cps (β)

cps (α)

<100 c (β)

cps (α)

10 cps (β)


Hand-held monitor alpha en beta Statistics - Optimalisation of measurement time

9

Detection limit (ISO11929) also given in KB 30-04-2010

k1- , k1-: Probability factor and

R0 : BG (cps)

t0 : BG measurement time (s)

tb: Sample measurement time (s)

Operational value CL (cps)

CL: Clearance Level (Bq/cm²)

R0 : Surface ‘seen’ (cm²)

glob: Global efficiency (isotopic vector %)

b0

2

β1α1

b0

0β1α1t

1

t

1.kk

4

1

t

1

t

1R.kkdétection de Limite

global.vue S CL(Bq/cm²) (cps)CL


High BG response - Increase

measuring time (CL: 0.4

Bq/cm²)

Trouble if…

Pre-characterization pipe

contaminated inside (gamma

emitters inside)

Clearance room with gamma

sources ‘next door’.

Method of the plate

(extensive)

If not homogeneous BG +

measure on each point

In-situ measurement place

not ideal. E.g. movement of

waste container arround

Hand-held monitor alpha en beta Influence gamma/BG

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Min. Infl. Max. infl.

Surface 170 cm² 170 cm²

Co-60 15% 15%

ALARM CL 10 cps 10 cps

Gamma

1 µSv/h

100 cps (β) 10 cps (β)

Meas. times 15 sec 3 sec


Same surface, same BG

Different efficiency for Co-60

CL: 0.4 Bq/cm²

… Measurement time

Hand-held monitor alpha en beta Efficiency

11

Min. Eff Max. Eff.

alpha/bèta

alpha/bèta

Surface 100 cm² 100 cm²

Co-60 10% 17%

ALARM CL 4 cps 7 cps

BG 10 cps (β) 10 cps (β)

Meas. times 10 sec 4 sec


Double effect on

Area covered (600 cm² - cover 6 times the area of a 100 cm²)

Measurement time 6 times smaller (Better statistic - Signal/BG)

…..But consider

Accessibility (too big for small corner e.g. ‘I’ shape beam)

Dilution (‘Richtlijnen meetprocedures’ – Maximum surface to be

measured = 1 m²)

Hand-held monitor alpha en beta Influence of the surface f.i. 600 cm² – 100 cm²

12

600 cm² 100 cm²

BG 50 cps 8 cps

Co-60 (eff.) 15 % 15 %

Operational CL 36 cps 6 cps

Measuring time 0.56 sec (1 sec) 3.4 sec (4 sec)


Ergonomics factors :

Electronic + probe together ?

Sound (alarm load enough & sound increase with level of activity)

How fragile ?

Number of options - How smart ?

Go – no go alarm

Indication in Bq/cm² or cps,

Isotope library,

Automatic update with BG,..

Blocking options (easy to use – no risk of changing setup)

Hand-held monitor alpha en beta Other consideration when selecting a device

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Interference (searching for non existing alpha’s)

Operator – basic training (go – no go)

Optimize the measurement time

Influence of BG (gamma’s)

Pre-characterisation – problem in contaminated area’s (with gamma emitters)

Clearance measurement - Problem of BG fluctuation

Nuclide vector will decide which detector

At least can measure it (C-14)

Best efficiency

Surface

Measurement time

Accessibility

Max 1 m²

Hand-held monitor alpha en beta Conclusion

14


Types:

Hand held monitors

Gross counting

Spectrometry

Gamma camera

Huge variety (from very simple to extremely complex)

All sort of shapes

All sort of calculation algorithms

Direct measurement Gamma teller - content

15


Pre-characterisation

Energy range can vary (X-ray & low energy - typically starts at 7 keV –

60 keV)

Direct measurements - Gamma Hand held

16

Pastic scintillator

From 50 nanoSv/h GM tube

From 0.1 µSv/h – 1 Sv/h

Telescopic for high dosis


Advantage

Fast detection. E.g. 20 kg, Co-60/Cs-137 needs

like 30 second

4 pi geometry - Not really sensitive to geometric

distribution activity

Operator: Basic training(Go-no go)

Disadvantage

Limited in space (cut material)

Bulk measurement no spectrometry BUT

algorithm to

Measure Co-60 (CCM or ROI)

Compensate for natural activity (portmonitor)

- concrete

Direct - gamma Gross counting – 4 pi geometry + Shielding

17

Spectra of Plastic-Detectors (22x22cm2; d=10cm)

0

5

10

15

20

25

30

35

40

45

50

0 500 1000 1500 2000 2500

Energy in keV

Rn

et(C

o),

Ba

ckg

rou

nd

in

1/s

0

20

40

60

80

100

120

140

160

180

200

Rn

et(C

s) i

n 1

/s

7*Background Co-60 Cs-137


Out of 4 pi geometry

Efficiency depends on position (sum of

solid angles)

Level of conservatism in parameters

OR Alarm + x sigma

Less shielding

Higher detection limit

Effect of fluctuation (number of BG to

meas.)

BUT

Better flexibility in material that can be

measured.

Can measure material in ‘same

geometry – e.g. walls with surface

contamination

Direct - gamma Gross counting less geometry – less shielding

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60°

180°


Direct - gamma In-situ gamma spectrometry

Gamma imaging

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Detectors

Scintillatores (e.g. NaI, LaBr3)

Seminconductors (e.g. CZT, HPGe)

Measurement

Gamma spectrometry

Individual radionuclides


Direct - gamma Detector material

NaI (Tl) HPGe Cd(Zn)Te LaBr3

Resolution

662 keV40 keV 2-3 keV 18 keV 10 keV

Activity level

measurementRather low

From low to

rather high

From medium to

very highRather low

Cost Rather cheap Expensive Rather cheap Rather cheap

Remarks Thermal drift N2 CoolingSmall size

detector

Presesence

La-138

Traditional New

20


Direct - gamma In-situ gamma spectroscopy

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Method: gamma-spectroscopy, using semi-mobile and fully

characterised high purity germanium detector accompanied

with modeling tools to measure specific total gamma activity &

single RNs (Bq.g-1, Bq.dm-2)

Advantage

Large range of geometry to be measured (small and large

surfaces)

Direct results

Detailled information is obtained

In some cases: determination of activity depth

No gamma peak interferences (except X-ray radiation)

Disadvantage Long measurement time

Ambient dose rate should be low

“Semi mobile”


Direct – gamma Gamma camera

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Previous technique

Pin-hole camera

Compton camera

Long time 20-40 min

Image problem

Detection limit high

New generation

Multiple pin-hole

+ Code

Meas. time – 1 min – 10 min.

Detection limit: Hot spots of ~ 1 µSv/h in

contact

Radiation

source

Gamma-ray detector

(position sensitive)


Huge variety

From very simple to extremely complex

All sorts of shapes

All sorts of combinations

All sorts of calculation algorithms – might have black box effect validation

with real activity

… To be adapted to shape/type of material and isotopic vector

Direct measurements – Direct gamma Conclusion

23


Pre-characterisation:

Very often used to validate the theoratical isotopic vector and

establishing scaling factor – level of conservatism

For DTM - Measuring in alpha/beta, low alpha/beta energy – pure

beta energy

For Activation profiles

Clearance :

Not the preferred one BUT difficult to avoid for DTM like pure alpha

or beta emitters, Tritium,… if can not be scaled to an other key-

isotope

How Representative ? (Statistical approach: homogenous – zone

with high risk of accumulation of activity)

Expensive & long process

Indirect/destructive measurements When ?

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Taking the sample

Treating the sample

Measuring the sample

Indirect/destructive measurements 3 steps approach

25


Indirect/destructive measurements Taking the sample

Smear/wipe (Non-fixed contamination – how much

is on the wipe ?)

Scratch sample

Shave sample

Direct mass sampling (drilling, hammering, sediments, etc)

Core drilling

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Indirect/destructive measurements Treating the sample – prepare for measurements

Drying

Grinding, milling, crushing

Combustion

Dissolution

Radiochemistry separation

Preparation for measurement

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Indirect/destructive measurements Measuring the sample

Alpha or beta total (using ZnS global) – smear or on precipitate

Alpha spectrometry (PIPS):

After radiochemical separation: Th-232, U-234, U-238, Pu)238, Pu-239/240,

Am-241, Cm-242, Cm-243/244

Direct on the wipe if not wet (absorption)

Liquid scintillation counting (LSC)

After radiochemical separation: H-3, C-14, Cl-36, Ca-41, Fe-55, Ni-63, Sr-90, Pu-241

H-3 – on extraction from smear test

Gamma spectrometry: Geometry of the sample important

Mass spectrometry (ICPMS):

Th-232, U-234, U-235 and U-238

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-100

-80

-60

-40

-20

0

0,1 1 10 100 1000 10000 100000

Specific activity (Bq.g-1)

Depth (mm)Cs-137

concrete

mortar

fly ash

concrete

paint

epoxy

Sampling & analysis Core drilling-gamma spectrometry Nal

29


Expensive & long process

Used a lot in Pre-characterisation

Can not be avoid for DTM’s like pure alpha or beta emitters,

Tritium,… if can not be scaled to an other key-isotope

How Representative ?

Statistical approach: homogenous

Homogeneisation of rubbels

Indirect/destructive measurements Conclusion

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NPP, research reactors, fuel industry

Full nuclide vector (from pre-characterisation) – per ‘group’

Eliminate the one that contributes less so that the sum formula < 0.99 Art

11: 30/04/10 Richtlijnen meetprocedures – art 11 4°

Le vecteur isotopique peut être limité aux radionucléides les plus significatifs, c'est-à-dire les

radionucléides dont la contribution commune dépasse 99 % lors de l'application de la règle de la

somme décrite à l'annexe IB au règlement général.

DTM still in that list ? If so

Spectrometry: Scaling factor from key nuclide Co-60 – Cs-137 or to Am-241

Bulk measurement: take them into account using average efficiency based on %

Labs with multiple experiences or in medical sector

pure beta: P-33; Cl-36, Sr-90,…

pure gamma: Se-75, Cd-109,…

Link with daughter product

Link between isotope ?

Phase 1: Pre-characterisation Nuclide vector – Finger print

31


Group by materials, geometry, nuclide vector in a

‘scope’

Each scope has its measurement methodology

Try to cover all materials

Phase 2: Developing measurement strategies

32


Porous versus smooth surface - (contamination

penetrate or not)

Alpha measurement big concern

Gamma matters less

Flat versus complex geometry

Alpha/beta measurement big concern

Gamma matters less

Painting, rust, physiochemical form,…

Alpha/beta measurement big concern

Gamma matters less

Developing measurement strategies Classification - Type of material

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Deliberate dilution by adding ‘clean’’ wastes in order to stay bellow

clearance level is NOT ACCEPTABLE (art 34.2 ARBIS)

Never the less,… Unavoidable dilution may occur, and is ACCEPTABLE.

Averaging value (measure) Homogeneity (extracted quantity) Max. 1 ton en 1 m3 Art 11: 30/04/10

Richtlijnen meetprocedures

RP 113/114 – Bq/cm²

Developing measurement strategies Dilution

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Where ?

Building material (bricks tiles– K-40, – plasterboard Ra-226),

Sand

NORM material (e.g. ‘Plaques disjoncteur: ciment amiant réfractaire’)

Legislation

Art 11: 30/04/10 Richtlijnen meetprocedures: Don’t have to take into

account if it doesn’t come from the installation. Level’s: K-40 = 1; Ra-226+:

0.01; Th-230: 0.1; Th-232: 0.01

Arrêté AFCN 01/03/2013 (MB 25/03/2013) - Special diposal ? If K-40: 5; Ra-

226+: 0.5; Th-230:10; Th-232:5

When is it a problem ? In bulk measurement (establish a natural BG value) versus energy selective

monitoring e.g. spectrometry

Developing measurement strategies Natural radioactivity

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High level of confidence in technique & methods (validation)

Which degree of complexity

Think sustainable:

Segregate dangerous material

Decontamination could generate more waste

Minimise risk,..

Human factor

Error (handheld monitor more sensitive)

Financial (Other alternatives)

Developing measurement strategies Other considerations

36


Huge selection of devices on the market – possibility to combine

Measurement devices can be tricky

There is not one recipe to create methodologies

Inspiration from other projects

Balance the pre-characterisation data & measurement techniques for

grouping material

Conclusion

37

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